The present invention relates to an objective lens actuator and, more particularly, to an objective lens actuator including a collision avoidance mechanism that is provided on a lens holder equipped with an objective lens as an optical element.
In an optical disk drive for use with discs, such as a compact disc (CD), a multipurpose digital disc (DVD), a high-definition DVD, a Blu-ray disc (BD), and the like, a recording surface of the disc serving as a recording medium is irradiated with an optical beam, whereby information is recorded and reproduced.
In an objective lens actuator constituting an optical system of a recent optical disk drive, in order to optically process a high density disc such as a BD, a wavelength of the light source is made short (e.g., 405 nm for the BD), and a numerical aperture (NA) of an objective lens is increased (to; for instance, NA=0.85 for the BD), thereby making a spot of the optical beam focused on the recording surface of the disc small. When the numerical aperture of the objective lens is increased as mentioned above, a working distance (WD) which is an opposed distance between the objective lens and the disc surface achieved when the disc is optically processed by the objective lens actuator has hitherto been known to become extremely small.
Some of objective lens actuators hold a lens holder in a cantilever manner by a suspension wire that extends from a fixed member and that is made of a conductive thin wire having elasticity. In the objective lens actuator of this type, the lens holder having an objective lens is controllably displaced in both a focusing direction and a tracking direction by action of an electromagnetic drive mechanism along with flexural deformation of the suspension wire. Therefore, in the objective lens actuator requiring a very small WD as mentioned above, the disc surface may collide with the objective lens of the lens holder for any reasons (e.g., vibration and warpage of a disc), thereby causing flaws on the disc surface, a recording surface of the disc, or the surface of the objective lens.
To avoid such collision, the lens holder has hitherto been provided with a collision avoidance mechanism for preventing collision of the objective lens with the disc, which would otherwise be caused when the objective lens collides with the disc (see; Patent Document 1, Patent Document 2, and Patent Document 3).
Patent Document 1 discloses a plate-shaped collision avoidance member made of a material such as polyacetal. The collision avoidance member is inserted into a space defined in a lens holder from one side, whereby a tip end of the collision avoidance member is caused to project to the other side of the space. A protrusion provided on an end of the collision avoidance member is engaged with a stopper face provided on the other side of the space, thereby regulating the width of a projection of the collision avoidance member out from the objective lens.
Patent Document 2 describes protectors that are made of a POM-based resin material and formed at two locations along an edge of a lens barrel of an object lens provided on a lens holder so as to protrude out of the objective lens by outsert molding.
Patent Document 3 describes metal plates that are covered with a protective lubrication layer made of an amorphous carbon film, or the like and that are provided at a plurality of locations along an objective lens of a lens holder by the outsert molding so that the protective lubrication layer protrudes out of the objective lens.    [Patent Document 1] Japanese Patent Publication No. 2007-305179 A    [Patent Document 2] Japanese Patent Publication No. 2002-269790 A    [Patent Document 3] Japanese Patent Publication No. 2001-297478 A
However, in a conventional art described in Patent Document 1, a lateral width and a longitudinal width of the space are arranged to suit a lateral width and a thickness (a longitudinal width) of the plate-shaped collision avoidance member, whereby the collision avoidance member is inserted into the space without a backlash. When a plate-piece-shaped collision avoidance member is pinched and inserted into the space of the lens holder by tip edges of a jig such as a tweezers, the collision avoidance member becomes easily caught by an edge on one side of the space. Thus, there has hitherto been a problem related to an assembly, that even an experienced operator can not readily perform the inserting operation.
In the conventional arts described in Patent Document 2 and Patent Document 3, it is necessary to use a sophisticated molding technique such as the outsert molding in order to assemble the collision avoidance mechanism. Therefore, there has been an unavoidable problem of complicated assembly processes and an increase in cost.
In addition, a sheet-shaped protector has hitherto been stuck to positions around which the objective lens of the lens holder is set. However, the technique has a potential risk of the protectors coming unstuck from the lens holder. Thus, the technique encounters a problem with the reliability of an effect of preventing collision of the objective lens with a disc (a protecting effect).